The present invention relates to electric window lifters for motor vehicles, in particular window lift systems for frameless vehicle doors.
In particular in convertibles, frameless vehicle doors are used in which the vehicle window pane can be moved electrically out of the body of the door. In frameless vehicle doors, the rubber seal is not part of the door structure but instead attached to the vehicle roof. If the vehicle door is opened, the window glass must be automatically lowered somewhat in order to protect the seal from damage if the glass presses laterally on the seal. When the vehicle door closes, the window pane then moves automatically upward into the rubber seal to the stop.
However, there is a requirement that the movement distance by which the window pane is lowered is sufficiently large so that the upper edge of the window pane is located below the seal but not by more than 4 mm. These requirements are a component of safety rules which provide that an anti-trapping protection must be implemented during the closing of the window if the upper edge of the window pane is at a distance of more than 4 mm from the lower edge of the seal.
However, the anti-trapping protection cannot be activated if the motor which drives the window pane has not assumed a specific stable speed, and there is therefore the risk that it will not be possible to satisfy the safety requirements during the upward movement or the closing if the window pane is moved by somewhat more than 4 mm below the lower edge of the seal. If, on the other hand, the upper edge of the window pane is not lowered sufficiently below the lower edge of the seal, the seal can be damaged during the opening and closing of the vehicle door.
Furthermore, these requirements are to be complied with over a temperature range from −40° C. to 80° C.
Electric window lift systems usually have a DC motor as a drive motor, which is coupled mechanically to the window pane. The mechanical coupling comprises, inter alia, a linkage and a wire cable.
The position of the drive motor is determined using a Hall sensor which senses the number of revolutions of the drive motor. Owing to the mechanical coupling of the drive motor to the window pane, the number of revolutions corresponds to a movement distance of the window pane. It is therefore possible to estimate the position of the window pane on the basis of the revolutions of the motor sensed by the Hall sensor.
However, the number of measured revolutions of the drive motor does not always correspond to the precise position of the window pane, since the window pane does not also immediately move with the beginning of the movement of the drive motor, at least starting from the upper stop of said window pane. This is caused, inter alia, by the fact that the mechanical connection between the drive motor and the window pane has play and in addition contains the wire cable which cannot be completely tensioned at the time of starting of the drive motor. Furthermore, the extension of the wire cable depends to a great extent on the temperature and the aging, with the result that the determination of the position using the Hall sensor is not sufficient to determine in advance with sufficient accuracy the actual movement distance for the lowering of the window pane.
Document DE 100 15 856 A1 discloses a method for determining the residual running time of a drive until a stop is reached, wherein in each case the position of the window pane relative to a mechanical stop is sensed, the time difference between two incremental signal generator pulses in the vicinity of the mechanical stop is determined, and the remaining residual running time of the electric drive until the mechanical stop is reached is calculated.
The object of the present invention is to make available a method with which a window pane can be moved during the opening of a vehicle door, in such a way that the upper edge of said window pane is located in a region at a predefined distance, for example of less than 4 mm, below the seal.